On Twitter, I argued that this would have been the wrong venue for such a debate question because the most consequential impacts from climate extremes (whatever mix of forces triggered them) and the vast majority of growth in greenhouse-gas emissions are outside United States borders. Global warming, both in its most significant drivers and consequences, remains a global issue.

Of course that doesn’t mean there’s nothing to focus on domestically; there are huge opportunities to spur advances in low-carbon energy technologies and energy conservation that could pass muster with a broad range of Americans. And building resilience to climate extremes — from drought to flooding to destructive storms — is a nonpartisan no brainer.

But in the context of greenhouse-driven climate change, too much of a focus on domestic policies or legislation can obscure bigger realities:

There are two more presidential debates addressing both foreign and domestic issues. What would you ask, if there’s a chance for a question related to climate and energy?

One question from me would be:

While persistent and deep uncertainty surrounds the most important potential impacts from and responses to greenhouse-driven global warming (see David Roberts, Michael Levi and this list of reviewed research for more), the long-term picture of a profoundly changed Earth is clear. What do you see as the best mix of achievable policies to limit environmental and economic regrets?

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.